Avoided Crossing Patterns and Spectral Gaps of Surface Plasmon Modes in Gold Nano-Structures

TL;DR

This study investigates how ultrashort laser pulses interact with gold nano-structures, revealing mode coupling effects, avoided crossing patterns, and spectral gaps in surface plasmon modes influenced by structural configuration.

Contribution

It introduces a detailed analysis of surface plasmon mode interactions and avoided crossing phenomena in gold nano-structures under ultrashort laser pulse excitation.

Findings

Observation of energy and momentum gaps in plasmon modes

Identification of mode switching from dark to bright modes

Dependence of spectral features on nano-structure configuration

Abstract

The transmission of ultrashort (7 fs) broadband laser pulses through periodic gold nano-structures is studied. The distribution of the transmitted light intensity over wavelength and angle shows an efficient coupling of the incident p-polarized light to two counter-propagating surface plasmon (SP) modes. As a result of the mode interaction, the avoided crossing patterns exhibit energy and momentum gaps, which depend on the configuration of the nano-structure and the wavelength. Variations of the widths of the SP resonances and an abrupt change of the mode interaction in the vicinity of the avoided crossing region are observed. These features are explained by the model of two coupled modes and a coupling change due to switching from the high frequency dark mode to the low frequency bright mode for increasing wavelength of the excitation light. PACS numbers: 73.20.Mf, 42.70.Qs, 42.25.-p,